Dr John
by TheMadKatter13
Summary: [TTF 51/SWN 06] Anonymous said: For the prompt: John and Sherlock are both underage and John convinces Sherlock to let him "play doctor" so he can "have practice" when he goes to medical school one day. [Full Summary Inside] AU; Top Teen John / Bottom Shota Sherlock


**SUMMARY: Anonymous said: For the prompt: John and Sherlock are both underage and John convinces Sherlock to let him "play doctor" so he can "have practice" when he goes to medical school one day. Sherlock is totally oblivious and goes along with it, and it's not until John's fingers are buried in his arse that he realizes what is really going on. Their level of previous sexual experience is in your smutty hands.**

 **AO3 TAGS: Alternate Universe, Established Relationship, Underage John, Teen John, Underage Sherlock, Shota Sherlock, Underage Sex, Medical Kink, Doctor/Patient, Top John, Bottom Sherlock, Anal, Anal Fingering, Anal Sex, Spitefic**

 **AN: Well, we almost made it back to familiar territory; we took the 'I Ship It' exit but then we ended up on the 'Not My Kink' turnpike somehow. Still, hope I did it justice. Sorry it took so long, Anon!**

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"Thanks again for doing this on such short notice, John," Mummy was saying in the atrium as she tugged on her coat. Even from his spot at the top of the stairs, watching from between the balustrade, Sherlock could see the signs of stress on her. He didn't mind though. He'd be worried too if someone called to tell him that his mum was in the hospital. "Mycroft is still away at boarding school and won't be back till spring otherwise we'd have him-"

"It's alright, Mrs. Holmes," John assured with a warm smile that never failed to make Sherlock blink. "You go look after your mum. Mine doesn't have a problem letting me stay the night and taking Sherlock to school in the morning."

"You really are a godsend, John." There was a small quiver in her voice that made Sherlock uncomfortable but he didn't know why.

There was a honk of a horn from outside and Mummy glanced out the door where Father was already waiting in the car. Then her gazed turned towards him and Sherlock nodded his head. She smiled at him, then again at John, and then she was out the door. John stood in the doorway for a long time, staring into the falling darkness as the red glow of the tail lights faded, and Sherlock crept down the stairs to stand behind him. When John finally stepped back and closed and locked the door, he first turned to look up the stairs where Sherlock had been, and then down, where Sherlock was.

"What do you want to do first?" John asked him with that warm smile of his that made Sherlock's heart do something peculiar.

"Did you need to do your doctor practice?" Sherlock asked him, eyes already scanning down John's body, searching for the little things only he and Mycroft seemed to be able to see.

Something changed in John's smile, and Sherlock shivered. "Of course," he said with a nod. He held out his hands and Sherlock raised his arms to be picked up - he didn't normally like to be carried, he was too old for that now, but John was warm and solid from his rugby games, and Sherlock liked the feel of him a different way than he like the feel of his mum and dad. "Let's get our patient ready."

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Sherlock was a big boy now, but John was bigger. And older. Almost as old as Mycroft. Which wasn't that old, in the grand scheme of things. Nowhere near as old as mummy and daddy, but John was already in secondary school, and he'd be well into uni before Sherlock even joined secondary himself. But it was because he was so close to university that he had to practice for being a doctor. He'd wanted to be one almost his whole life, and Sherlock wanted for him to become one. And then when Sherlock was a world-famous consulting detective, John would be his doctor.

"Arms out," John said, voice soft and warm, his smile even warmer, and his hands even warmer than that when their calloused palms pressed to the bare skin of Sherlock's ribs.

Obediently, he raised his arms out to the side, sliding them across his bedspread, like he was making a snow angel like John had taught him last winter.

"Good boy," John praised, sliding his hands down the length of Sherlock's arms. The callouses made Sherlock's arms feel funny, but he knew he wasn't supposed to move, so he shook off the shiver they gave him. It was a little harder to do when the hands went back up his arms, and then down his body, over his bare belly and down his bare legs.

"And legs out," John said, large hands falling away from Sherlock's ankles.

Even though it made his face hot, to spread his legs and expose himself like this, he did as John had asked

He moved his feet as far apart as they would go on the bed, until he was lying like a starfish, naked and stretched out, on top of his sheets. The duvet had already been pushed to the floor, "to keep from getting dirty," John had reminded him.

"Vey good," John murmured. "Let's check your thermometer."

The first touch to his penis, a simple brush of the callous on John's thumb, from tree climbing, Sherlock had long ago deduced, made Sherlock shiver intensely. He couldn't help the way he curled in on himself, the touch still new and familiar, even though this wasn't the first time John had practiced doctoring on him. He didn't wait for John to raise his eyebrow at him before he forced his arms and legs back down to the bed, and he got a kiss to his lips in reward.

"You don't seem very warm just yet," John commented, tapping on the tip of Sherlock's penis with the pad of his index finger. It was true, Sherlock's penis was still mostly soft, small between his legs, nowhere near the size of John's cock, which was thick and long and already standing straight out. "Let's fix that."

Sherlock opened his mouth to respond, to say what, he couldn't have said, but then John started to stroke him, just two fingers curled around Sherlock's penis and thumb pressed to the underside in a slow pull. It made him act like a marionette, pulling his back off the bed, and then pushing it back down, following the tide of John's hand. He shuddered and shook as John kept at it, until his penis was hard and straight, though it was only a fraction of John's size.

"Such a good boy you are for me, Sherlock," John said, finally pulling away and leaving Sherlock shaking on the bed, fingers curling in the sheets to keep from closing his arms against John's ministrations. "The perfect patient." His face flushed hot from the praise, but he didn't have time to formulate a response, if he could have. John was dripping lubrication onto his fingers. "Let's get you prepared for the big boy thermometer."

Sherlock nodded, but John was no longer looking at him. Instead, his eyes were fixed on the lube he was pouring onto his fingers, working between them to warm up the cold liquid. Still, Sherlock jumped when John's wet fingers traced his sphincter, massaging the muscle until the tip of John's finger sunk in.

"Let's check your prostate before we check your temperature," John said with a grin, and then proceeded to work Sherlock open with the sort of patience that made it easy to see how he'd made rugby captain.

This part was always difficult, when those thick fingers were twisting inside of him, searching, and Sherlock's mind didn't know what to do with the stimulation, when his brain didn't know how to process it. He twisted and he turned on the sheets, he curled his fingers in his pillow and pulled it over his face as he whimpered, he writhed, but John just kept holding him down until at last he pulled his fingers free and Sherlock fell to the bed panting, his chest heaving.

"Your such a perfect little patient, Sherlock. I hope all my patients when I grow up are as good as you are." John's praise was a warmth in Sherlock's belly that lit him up from the inside like a Christmas fire in the fireplace. Or maybe that was the prostate exam talking.

"Th-thank you, John," Sherlock managed to stutter.

John lightly slapped the outside of Sherlock's thigh as he spread Sherlock's legs and shuffled up between them. "What are you supposed to call me when we play doctor?"

"Thank you, Dr. John," Sherlock corrected obediently.

"You're welcome." John's voice was warm, sinking into Sherlock's belly like a cup of cocoa, and he smiled even as he dropped his eyes from John's.

His legs looked even smaller on the either side of John's thick waist, thinner than his arms, and he wondered if he was ever going to catch up. John wasn't done growing yet, but Sherlock had barely started.

"Are you ready to get your temperature checked?" John asked, something strange to his smile, like always.

Sherlock's heart beat hard in his throat but he still nodded and reached up and back to tightly fist his pillow.

"Alright, then let's get that thermometer in," John said, the tip of his penis a heavy weight against Sherlock's sphincter. He inhaled deep and the breath stuck in his throat as John started to push in, and John had to pause to remind him "Don't forget to breathe and relax, Sherlock. My thermometer will never fit if you don't."

It took a few tries to remember how to expel the air from his lungs, but when he did, John gave him another one of those warmth-inducing smiles, and started pushing again. He didn't stop again, not when Sherlock stopped breathing when the pressure started becoming intolerable, or when it did become intolerable and tears rolled down Sherlock's cheeks, his arms wrapping tight around John's neck as his body tensed at the pain. He didn't start until his hips were so flat against the back of Sherlock's that Sherlock's skin was tickled by the thatch of hair at the apex of John's legs that Sherlock hadn't grown yet.

"What a good boy, Sherlock," John was murmuring, big hands stroking through Sherlock's hair. "My perfect patient. You take my co- my thermometer better and better every time we practice. My perfect boy."

Sherlock could only tremble and nod, his penis hard between his legs, as he tried to adjust to the thick length in him. It was getting easier, but it was still such a strange thing that he still didn't know how to handle it.

"Are you ready?" John asked, after a long minute of quiet, soothing sounds and calming fingers through Sherlock's curls.

He wasn't, but John needed to finish his exam, he got antsy when it took too long, so he nodded. "Yes, Dr. John," he managed, though his voice was a little weak.

"Good boy. Let's get the thermometer turned all the way on," John said, and then he pulled his hips back, his penis pulling out, before he pushed back in.

Sherlock jerked and whimpered at the sensation, but John didn't stop that time either. He didn't stop when Sherlock did the same thing on the next pull out-push in, or the one after that. He just kept smiling that soft smile, the one that meant that he was pleased with Sherlock, and Sherlock hung onto that image even when he began to feel weird. So weird that he tried to pull himself away from the feeling, tried to push John off, to completely disengage his penis. But John just smiled even more warmly and carefully settled his weight over Sherlock to keep him pinned.

"John, John," Sherlock panted, tossing his head from side to side, feeling physically and mentally confused.

"You're so tight and hot, Sherlock," John murmured, his hips starting to pick up speed, intensifying the strange feeling in Sherlock's belly and spine. "But you're not hot enough yet. Just a little bit more and the thermometer will go off."

Sherlock bit his lip to keep from crying out, or to keep from crying, and just nodded, tightening the circle of his arms around John's neck. They got even tighter as each stroke pushed harder and faster into him, and he had to dig his nails into his forearms to keep from digging them into John's back.

Grunts of hot air pressed against his throat with each thrust, and with each thrust, a whimper was forced out of Sherlock's mouth. He couldn't help it. He'd tried to stop, both now and before, but he couldn't help the strange little noise, like he'd become a dog toy. He didn't like it, but he thought John did, because the louder he got, the gruntier John got, the more John's chest against Sherlock's vibrated with low, deep moans.

"Yes, Sherlock, yes, just like that," John whispered. Sherlock didn't know just like _what_ , but he nodded anyway. "Are you ready? You're at peak temperature and my thermometer is about to go off. Are you ready, Sherlock?"

"Y-yes," Sherlock stuttered. "Yes, J- Dr. John."

"Good boy," John murmured. And then again. And again and again and again, a soft litany in Sherlock's ear until John pushed forward so hard that it hurt and Sherlock tensed, a full-body cringe that made John groan and curl tight around him. "So so good, Sherlock."

Sherlock whimpered at the pressure against him, and it took a long moment, but John sat back on his heels, his forehead resting against Sherlock's shoulder as he breathed against Sherlock's skin and his release dripped down the back of Sherlock's thighs. Finally, he sat up, smiling, and Sherlock smiled too, feeling relieved.

"What a successful checkup. Good job, Sherlock," he said, ruffling Sherlock's hair. "And now, my payment." Sherlock's smile made it hard to purse his lips, but he finally did it, and John leaned forward to press a kiss to them. "Good boy. And what do you say?"

"Thank you for my checkup, Dr. John," he said obediently, and he got a warm smile in turn that made him smile even wider.

"That's my perfect patient," John praised, picking Sherlock up and walking him to his en suite. "Now let's go get you ready for bed. And don't forget, this is our secret practice. Do you remember why?"

Sherlock nodded. "Patient confidentiality!" he cheered.

"That's right," John said, sitting in the bathtub with Sherlock in his lap, situating him just right before leaning forward to turn the taps. "Patient confidentiality."

FIN

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 **I only learned fairly recently, like within the last year, that when people said "playing doctor", it was not… non-sexual. So that was news.**

 **Like the thing? Reblog the thing (themadkatter13fanfiction tumblr, /tagged/Dr.-John).**


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